Metal-air batteries are electro-chemical reactors that produce electric current by oxidizing metal with oxygen. These reactors can have high energy densities and be relatively inexpensive to produce. Metal-air batteries may be used to power various items such as hearing aids, cameras and electric vehicles.
A metal-air battery may include a mass of metal that forms a porous anode that is saturated with an electrolyte. During discharge, oxygen reacts at a cathode to form hydroxyl ions that migrate into the metal/electrolyte paste to form a metal hydroxide, releasing electrons to travel to the cathode. The metal hydroxide decays into metal oxide and the resulting water returns to the electrolyte. The water and hydroxyls from the anode are recycled at the cathode, so the water is not consumed. The reverse process can also occur. During charge, electrons react with the metal oxide and water to reform the metal, releasing hydroxyl ions that migrate to the cathode. The hydroxyl ions are then oxidized to oxygen gas and water.